Liquid hydrocarbon mediums, such as crude oils and crude fractions, including naphtha, gasoline, kerosene, jet fuel, fuel oil, gas oil and vacuum residuals, often contain contaminants that can be deleterious to either refinery processing or product quality. The contaminants can contribute to corrosion, heat exchanger fouling, furnace cooking, catalyst deactivation and product degradation in refinery and other processes. The contaminants are broadly classified as salts, bottom sediment and water, solids and metals. The amounts of these impurities vary depending upon the particular crude and its processing.
Desalting is a process that is used to remove contaminants, primarily inorganic salts, from crude oils prior to refining. The desalting step is provided by adding and mixing with the crude a few volume percentages of fresh water to contact brine and salt. Desalting provides benefits to the processing or refining of crude oils, including, reducing crude unit corrosion; reducing crude preheat system fouling; reducing the potential for distillation column damage; reducing energy costs; and reducing downstream process and product contamination.
In crude oil desalting, an emulsion of water in oil is intentionally formed with the water admitted being on the order of about four (4) to about ten (10) percent by volume based on the crude oil. Water is added to the crude and mixed intimately to transfer the impurities in the crude to the water phase. Separation of the phases occurs due to coalescence of the small water droplets into progressively larger droplets and eventual gravitational separation of the oil and underlying water phase.
In U.S. Pat. No. 4,778,589, a process is disclosed for the removal of metal contaminants, particularly calcium, from hydrocarbonaceous feedstocks. The process comprises mixing the feedstock with an aqueous solution of a metals sequestering agent, particularly hydroxycarboxylic acids, and more particularly, citric acid, then salts or mixtures thereof, and separating the aqueous solution containing the metals form the de-metalated feedstock.
U.S. Pat. No. 5,078,858, discloses and claims methods for extracting iron species, such as iron naphthenate and iron sulfides from a liquid hydrocarbon, such as crude oil. A chelant selected from the group consisting of oxalic or citric acid is added directly to the liquid hydrocarbon and mixed therewith. The wash water is added to form a water in oil emulsion, the emulsion is resolved, and the iron laden aqueous phase is separated.
In US patent application publication no. US 2004/0045875 A1, it was found that metals and/or amines can be removed or transferred from a hydrocarbon phase to a water phase in an emulsion breaking process by using a composition that contains water-soluble hydroxyacids. The composition may also include at least one mineral acid to reduce the pH of the desalter wash water. A solvent may be optionally included in the composition. The process permits transfer or metals and/or amines into the aqueous phase with little or no hydrocarbon phase under-carry into the aqueous pHs.
Accordingly, a need still exists for a process that would show an improvement over the extraction of the contaminants in the crude oils such that the contaminants are not partitioned into the crude in the desalting process, using components that are water soluble, do not result in acids in the crude unit overhead that can raise neutralizer demand, are stable at high temperatures and that are easy to implement.